Bacterial blight of rice, caused by the pathogenic bacterium Xanthomonas oryzae pv. oryzae (Xoo), is one of the most devastating rice diseases, often resulting in yield losses of up to 50% and sometimes destroying an entire crop. The outcome of this disease is largely dictated by a few transcription activator-like (TAL) effectors that are secreted from bacteria into host rice cells. These TAL effectors bind to endogenous promoters and activate expression of corresponding disease susceptibility (S) genes. Such TAL effectors are essentially virulence factors of the pathogenic strains, and the host S gene induction is required for the plant to become susceptible to the disease. Thus the components of this disease complex represent a target for intervention. Complicating intervention strategies, the S genes are critical to plant survival and play an important role in growth and development in rice, making typical knockout strategies inappropriate.
The known TAL effectors of essential virulence include PthXo1, AvrXa7, PthXo3, and PthXo2 in a variety of Xoo strains, while the corresponding S genes are s11N3, Os8N3, and Os12N3 of the N3 family of rice. Naturally occurring genetic variations within the promoter regions of Os8N3 and Os12N3 prevent their inducibility and have been found to confer resistance to the strains that depend on the respective PthXo1 and PthXo2 for virulence in the otherwise susceptible rice cultivars. There is no known genetic variation in Os11N3 that confers disease resistance to AvrXa7 and PthXo3-dependant Xoo strains.
TAL effector nucleases (TALENs), fusion proteins of the DNA cleavage domain of endonuclease FokI and the various forms of TAL effectors (native or custom-made, truncated or complete), have quickly emerged as efficient endonucleases to direct double-strand DNA breaks and induce genetic alterations at pre-selected loci in presumably any eukaryotic organism.
A need exists in the art for plants that are resistant to Xanthomonas oryzae pv. oryzae (Xoo).
It is an object of the present invention to provide mutations in the Os11N3 promoter region that cause resistance to Xoo while still retaining plant growth and plant reproduction.
It is further object of the present invention to provide mutations in the promoter regions of other S genes, either individually or tandemly, that cause resistance to Xoo while still retaining plant growth and plant reproduction.